An aircraft in flight generates vortices (or wake turbulence) in its wake. The term vortex (or wake turbulence) is understood to mean aerodynamic turbulence (or a vortex) that forms downstream of an aircraft in flight.
An aircraft in flight primarily generates two vortices in its wake. These two vortices start at the wing tips and form due to pressure differences between the lower surface and the upper surface of the wing that cause a deflection of the air flow at the wing tip. These vortices at the wing tip are counter-rotating vortices and are characterized by a wind field that rises overall outside of the vortices and that falls overall between the vortices.
The wing tip vortices start from the wing tips and extend behind the aircraft and along the path just flown by the aircraft. The wing tip vortices tend to initially move towards each other and thereafter maintain a a constant separation from one another while at the same time losing altitude with respect to the altitude at which they were generated.
Formation flying allows a following aircraft to exploit the updrafts caused by the vortices of the leading aircraft. An advantage of exploiting the vortices is reduced fuel consumption by the following aircraft. However, situations may arise during a formation flight due to a maneuver or other minor event in which a following aircraft should move away from a vortex(ies) of the leading aircraft. Moving away from the vortices results in the following aircraft losing the updraft of the vortex(ies) and the benefits of the updrafts and lower fuel consumption.